Fusible protective device



Aug. 22,

Filed Jan. 27, 1964 United States Patent 3,337,705 FUSIBLE PROTECTIVE DEVICE Erwin Salzer, Waban, Mass, assignor to The Chase-Shawmut Company, Newburyport, Mass. Filed Jan. 27, 1964, Ser. No. 340,380 5 Claims. (Cl. 200120) This invention is concerned with electric fuses, and more particularly with synthetic resin encapsulated fuses including a pulverulent arc-quenching filler.

This type of fuses is particularly desirable for a number of reasons. The presence of a pulverulent arc-quenching filler tends to result in generation of relatively high arc voltages, and the outer casing or shell formed of a synthetic casting resin forms a gas-tight enclosure safely precluding any escape of hot products of arcing from the space inside of the casing or shell. Another advantage of fuses of the aforementioned type consists in that terminal caps or ferrules can be dispensed with, and in that the synthetic resin casting of which the casing is made can be used for firmly maintaining in position the contacts of such fuses, e.g., their stab contacts, or blade contacts.

Heretofore, in order to encapsulate fuses including a pulverulent arc-quenching filler, e.g., quartz sand, as a general rule a binder had to be added to the filler, whereby the compound formed of filler and binder was rendered self-supporting. Such a compound has a much smaller arc-quenching ability than a pure granular arc-quenching filler, i.e., than a granular filler with no binder added to it.

It is, therefore, one object of this invention to provide synthetic resin encapsulated fuses not requiring the addition of any binder to the pulverulent arc-quenching filler thereof, i.e., having a binderless pulverulent arc-quenching filler.

It is possible to design synthetic resin encapsulated fuses having a pulverulent arc-quenching filler, and dispensing with a binder for the latter, if the pulverulent filler is enclosed in a special container which, in turn, is enclosed within a shell of casting resin.

Heretofore the cost of manufacturing synthetic resin encapsulated fuses which include a special container for the pulverulent filler in addition to an outer shell of cast ing resin were so high as to render such fuses unacceptable.

It is, therefore, another object of this invention to provide synthetic resin encapsulated fuses having a pulverulent arc-quenching filler and a special container for the pulverulent filler in addition to an outer shell of casting resin which fuses are relatively simple to manufacture and require but an inexpensive special container for the pulverulent arc-quenching filler.

Further objects and advantages of the invention will become apparent as this description proceeds, and the features of novelty which characterize the invention will be pointed out with particularly in the claims annexed to, and forming part of, this specification.

For a better understanding of the invention reference may be had to the accompanying drawing wherein:

FIG. 1 is a vertical section across a fuse embodying this invention taken along 1-1 of FIG. 2; and

FIG. 2 is a vertical section across the fuse shown in FIG. 1 taken along 22 of FIG. 1.

Referring now to the drawing numeral 1 has been applied to indicate a container formed of an organic sheet material as, for instance, paper, or a plastic foil, e.g. cellulose acetate. Container '1 has a lateral wall la and a lower end surface or bottom 1b arranged substantially at right angles to lateral wall 1a. Container 1 is substantially in the shape of a prism. A pulverulent arc-quenching filler 2, preferably pure quartz-sand, is arranged inside of container 1. Filler 2 extends up to the top edge of container 1 and defines an upper filler surface 2a. The structure shown in FIGS. 1 and 2 further comprises a pair of bar conductors generally indicated by reference numeral 3 which are substantially rectangular in cross-section. Conductors 3 have relatively widely spaced portions 3a arranged inside of container 2 parallel to the lateral wall 1a thereof and relatively narrowly spaced portions 3b arranged outside of container 1 and parallel to the lateral wall thereof. Conductors 3 further include converging portions 30 intermediate portions 3a and 3b. For the purpose of assembly the spacing between conductor portions 3a is maintained by a pair of insulating spacers 4a, 4b. Spacer 4a arranged adjacent the bottom of container 1 is in the form of a plate, whereas spacer 4b arranged adjacent the top of container 1 is in the form of a cylindrical post whose ends of reduced diameter project into bores 3d in conductors 3. Portions 3b of conductors 3 define shoulders 3e and are tapered at 3 to facilitate insertion thereof into a fuse holder. Each portion 3a of each conductor 3 is provided with a pair of grooves 3g receiving the ends of a plurality of multiperforated ribbon fuse links 5 which are preferably made of silver. Links 5 are arranged transversely to conductors 3 and conductively interconnect the latter. As seen in FIG. 2 links 5 are arranged in two parallel planes of which each is surrounded by filler 2.

The relatively wide spacing between portions 3a of conductors 3 determines the length of fuse links 3, and since fuse links 3 are relatively long, the arc voltage generated incident to blowing of the fuse is relatively high. The spacing between portions 311 of conductors 3 is smaller than that of portions 3a since the smaller spacing of portions 3b adapt these portions better to be used as stab or blade contacts, i.e. to cooperate with another pair of contacts not shown in the drawing. The structure of FIGS. 1 and 2 further comprises an integral shell 6 of casting resin, e.g. an epoxy casting resin, exposing the relatively narrowly spaced portions 312 of-conductors 3, enveloping all sides of container 1 and the content thereof and encapsulating the converging portions 3c of conductors 3. The shell or body 6 of casting resin forms a hermetic seal positively precluding venting of hot products of arcing to the outside thereof. There is no need of providing container 1 with a cover for separating the pulverulent filler 2 from the casting 6 which encapsulates all the parts situated inside of container 1. If desired such a cover might be added.

The parts 3, 4a and 412 form a sub-assembly or unitary structure which is held in position relative to container 1 by means of a jig or fixture while container 1 is being filled with pulverulent arc-quenching filler 2. The casting of shell or housing 6 is effected in a conventional manner by means of an appropriate mold, and curing of the casting resin is elfected inside of the mold.

The lateral wall of container 1 has a predetermined depth. The depth of container 1 makes it possible to accommodate inside of the same a relatively larger quantity of binderless quartz sand, and to thus achieve a relatively larger arc-energy absorbing capacity. The widely spaced portions 3a of bar conductors 3 project into container 1 a distance equal to a preponderant portion of said predetermined depth of the lateral wall of container 1. This makes it possible to interconnect portions 3a of bar conductors 3 by a relatively large number of equidistantly spaced fusible elements or fuse links 5, thus achieving a relatively high current-carrying capacity and evenly distributing the are energy dissipated inside the fuse through its body of quartz sand.

It will be understood that I have illustrated and described herein a preferred embodiment of my invention, and that various alterations may be made therein without departing from the spirit and scope of the appended claims.

I claim as my invention:

1. An electric fuse comprising in combination:

(a) a container formed of an insulating sheet material and including a lateral wall having predetermined depth and an end surface arranged substantially at right angles to said lateral wall;

(b) a binderless pulverulent arc-quenching filler inside to said preponderant portion of said predetermined depth of said lateral wall thereof;

((1) ribbon fuse links arranged inside said filler in two spaced planes parallel to two sides of said lateral wall of said container and conductively interconnecting said pair of conductors; and

(e) an integral capsule of casting resin exposing said second portion of each of said pair of conductors and enveloping all sides of said container including said said container; upper filler surface.

(c) a pair of spaced substantially parallel electric cOn- 4. An electric fuse comprising in combination:

ductors arranged at substantially right angles to said (a) a container formed of an organic sheet material end surface of said container, each of said pair of and including a lateral wall having a predetermined conductors including a first portion projecting into depth; said container a distance equal to a preponderant (b) a body of binderl quartz-sand i id id portion of said predetermined depth of said lateral tainer; wall thereof and submersed in said filler and a sec- (c) a pair of stab contacts extending substantially ond portion projecting out of said container and parallel to said lateral wall of said container from out of said filler; the outside thereof into said body of quartz-sand (d) fuse link means arranged inside said filler conduca distance equal to a preponderant portion of said tively interconnecting said pair of conductors; and predetermined depth of said lateral wall of said con- (e) an integral shell of casting resin exposing said tainer;

second portion of each of said pair of conductors (d) spacing means of insulating material for said pair and enveloping all sides of said container. of stab contacts arranged in said body of quartz- 2. An electric fuse comprising in combination: sand;

(9.) a container formed of an insulating sheet ma- (e) fuse link means arranged inside said body of terial and including a lateral wall a predetermined quartz-sand conductively interconnecting said pair depth and an end surface arranged substantially at of stab contacts; and right angles to said lateral wall; (f) an integral layer of synthetic resin exposing ends (b) a binderless pulverulent arc-quenching filler inside of said pair of stab contacts and completely encapsaid container; sulating said container.

(c) a pair of space strip-shaped electric conductors 5- An ele tric fuse comprising in combination:

having relatively widely spaced portions arranged in- (a) a container formed of an organic sheet material side said container parallel to said lateral wall the-reand including a late al ll having a predetermined of and relatively narrowly spaced portions arranged dept outside said container parallel to said lateral wall a b ndcrless body of quartz-sand inside said conthereof, and said pair of electric conductors further miner n g n pp r and surface substantially including converging portions intermediate said relaat right angles to said lateral wall; tively Widely spaced portions and said relatively nara P of Sta'b Contacts extending Substantially rowly spaced portions, said relatively widely spaced 40 parallel to said lateral wall of said container transportions projecting into said container a distance Y y across said pp Sand Surface and P j equal to a preponderant portion of said predetermg into Said container distance equal to a p mined depth of said lateral wall of said container; Ponderant Portion of Said predetermined p of (d) fuse link means arranged inside said filler con- Said lateral Wall of Said Contain;

ductively interconnecting said relatively widely Spacing means of insulating material Said P spacedportions of id i of conductors; d of stab contacts arranged inside said container and (e) an integral shell of casting resin exposing said submersed in Said y of q d relatively narrowly spaced portions of said pair of an integral layer of Synthetic resin eXpOSiIlg ends conductors, enveloping all sides of said container Said P Stab Contacts and Completely pand encapsulating said converging portions of said Sulating s'aidcontainefpair of conductors.

3. An electric fuse comprising in combination: References Cited (a; a prislrlnatic container formed of an organic insu- UNITED STATES PATENTS ating s eet material and including a lateral wall 1 having apredetermined d th; 6/1912 lfi 200-131 3,110,787 11/1963 Borzom 200- 120 (b) a binderless pulverulent arc-quenching filler inside .3 1.39 712 6/1965 Kozacka 200 131 SaId container defining a upper filler surface 31196321 7/1965 Hollmann etal. 200:120 stantrally at right angles to said lateral Wall; 3 281 555 |10/1966 Fister 200 a pair of spaced parallel electric conductors ar- *120 ranged substantially parallel to said lateral wall of FOREIGN PATENTS said container, each of said pair of conductors in- 169,480 8/1934 Switzerland,

cluding a first portion arranged inside said container BERNARD A. GILHEANY, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

H. B. GILSON, Assistant Examiner.

and submersed in said filler and a second portion projecting across said upper filler surface out of said container, said first portion of said pair of conductors projecting into said container a distance equal 

1. AN ELECTRIC FUSE COMPRISING IN COMBINATION: (A) A CONTAINER FORMED OF AN INSULATING SHEET MATERIAL AND INCLUDING A LATERAL WALL HAVING PREDETERMINED DEPTH AND AN END SURFACE ARRANGED SUBSTANTIALLY AT RIGHT ANGLES TO SAID LATERAL WALL; (B) A BINDERLESS PULVERULENT ARC-QUENCHING FILLER INSIDE SAID CONTAINER; (C) A PAIR OF SPACED SUBSTANTIALLY PARALLEL ELECTRIC CONDUCTORS ARRANGED AT SUBSTANTIALLY RIGHT ANGLES TO SAID END SURFACE OF SAID CONTAINER, EACH OF SAID PAIR OF CONDUCTORS INCLUDING A FIRST PORTION PROJECTING INTO SAID CONTAINER A DISTANCE EQUAL TO A PERPONDERANT PORTION OF SAID PREDETERMINED DEPTH OF SAID LATERAL WALL THEREOF AND SUBMERSED IN SAID FILLER AND A SECOND POSITION PROJECTING OUT OF SAID CONTAINER AND OUT OF SAID FILLER; (D) FUSE LINK MEANS ARRANGED INSIDE SAID FILLER CONDUCTIVELY INTERCONNECTING SAID PAIR OF CONDUCTORS; AND (E) AN INTEGRAL SHELL OF CASTING RESIN EXPOSING SAID SECOND PORTION OF EACH OF SAID PAIR OF CONDUCTORS AND ENVELOPING ALL SIDES OF SAID CONTAINER. 